The present invention relates to a cushioning article, and more particularly relates to an improved construction and method for making a cushioning article having good comfort and support qualities with reduced material waste. For example, in the present invention, the cushioning may be employed in furniture seat and back cushions and headrests, and throw cushions, or the like. The invention is particularly suited for production of a bed pillow.
A comfortable sleep-inducing support for a person's head, such as a bed pillow, must meet several demanding criteria. For example, the pillow must be of a shape to conveniently receive a person's head. It must feel soft to initial contact, while at the same time provide adequate support. It should be air permeable to allow the body heat to be dissipated. It should have resilience so that it can be restored to an initial shape when a person raises his head from a pillow. At the same time, resiliency should not be such that the pillow will "fight back" when one is attempting to seek comfort and rest for the head. The achievement of the aforesaid criteria in one pillow at an economical cost with readily available material has been a problem.
In the past, comfortable pillows have been obtained traditionally by filling a sewn case with selected down or feathers from various fowl. Goose down was considered, for example, the most desirable. The resultant bed pillow readily conformed to a person's head. This was accomplished in part by compaction of the feathers, and in part by a shifting of the filling material so as to provide the gentle cradling of the head with the desired degree of softness, support, and selected amount of resiliency. The pillow was capable of being returned to its original condition after use by the simple process of being "fluffed." However, the scarcity and high cost of feather and down has resulted in the need for an acceptable substitute for the conventional pillow.
One approach was to attempt to utilize synthetic fibers to simulate the natural feathers and down. In this regard, synthetic fibers, such as of polyester polymers, were produced to provide a variety of fiber fillings for bed pillows. The fiber filled pillow, however, had a serious disadvantage in that the synthetic fibers did not possess the permanent resilience which were characteristic of the feather or down. As a result, such synthetic fiber pillows tended to matt and lose some of their usefulness after a comparatively short period of time.
Another approach was to use foam rubber, which was developed in the late 1930's. This was accepted as an upholstery material of superior comfort and great permanence, but in its original form, it was too firm for a bed pillow. In the late 1940's and early 1950's, a process for making latex foam rubber was developed (Talalay, U.S. Pat. No. 2,432,353) which was capable of consistently producing a foam rubber of sufficient softness and light enough density to provide a practical and comfortable pillow. As a result, in succeeding years, latex foam rubber pillows, made in accordance with the above invention, were utilized world-wide, partially, because of their durability and non-allergenic characteristics. While the latex form provided the best foam pillow, the price of the foam rubber was sufficiently high that the industry saw the need for the use of a less expensive material.
Flexible urethane foams, which were introduced into this country in the mid 1950's were of sufficiently low price that they began to have increasing acceptance in the furniture cushioning industry and in foam mattresses as a replacement for the foam rubber. While the flexible urethane foams did not have the resilience characteristics of the latex foam rubber, the price advantage of the flexible urethane foams was sufficient to result in the wide spread adaption of the material for the furniture cushioning and mattress industries. However, attempts have been unsuccessful to make a satisfactory bed pillow by the use of such polyurethane foams.
One of the problems is that the filling of a foam pillow, whether latex or polyurethane, does not shift as does down or synthetic fiber. As a result, such foam pillows could not achieve stress-free cradling comfort for a person's head partially by rearrangement and partially by compression but rather had to rely entirely on deformation to achieve cradling comfort which is so important for the inducement of sleep. This shortcoming of foams in general was particularly a problem in using polyurethane foam, making polyurethane foam generally unacceptable for use in a pillow.
One of the particular difficulties of polyurethane foam relates to the difficulty of achieving the desired shape. The external shape of a pillow is important, and it is well known that the proper shape for a bed pillow is one which, in cross section in both the length and widthwise directions, is in the form of a flattened ellipse. Such shape is hereinafter referred to as a stereo-elliptical shape, but the production of such shape from polyurethane foam has been uneconomical. This is because it is extremely difficult to economically produce the desired stereo-elliptical shape from a large block of polyurethane foam without incurring a large amount of material waste. Moreover, automatic machinery capable of cutting a compounded curvature has not as yet been developed. As a result, multiple operations are required to even approximate the desired shape of the pillow.
A second problem with use of the polyurethane flexible foam material has been in achieving the desired balance between comfort and support. As employed herein, the terms "comfort" or "softness" mean the ability of the cushioning structure to deflect at the surface and conform to the body shape. This prevents a concentration of pressure on the body. The term "support" employed herein means the ability of the cushioning structure to hold the body in the relaxes position and allow free body movement by providing a firm base to push against. Support minimizes stress on the joints. The desired comfort or softness for a pillow for sleeping is provided if the pillow deflects 25% of its original height when a compressing load of 3 to 7 lbs. distributed over a flat plate 50 sq. inches in area is vertically applied to it.
While the pillow should be soft to initial contact, it still must be able to provide adequate support for the head. One parameter for such support is that the pillow would have sufficient resistance that, in order for the pillow to be compressed 65% of its original height, a load is required which is 21/2 to 3 times the load needed to compress it 25%.
The aforesaid support, which can also be referred to as the resistance of the pillow to "bottoming" is usually measured as the load at 65% deflection. The desired softness-to-comfort relationship can be expressed as the ratio of load at 65% deflection to the load at 25% deflection. Such ration, called SAG or SAC factor, provides an approximate slope of the curve above the usual softness reference point (i.e., 25% deflection). Such ratio defines not only the characteristic shape of the compression-deflection curve of the flexible foam material but also provides substantial information about the comfort providing capability of the material when employed for cushioning a person's head.
Conventional polyurethane foam did not have the desired load deflection characteristics. SAG factors at 1.5 to 1.9 were representative of the best polyether urethane foams based on polyoxypropylene ethertriols of 3,000 to 4,000 molecular weight and an 80-20 isomer ratio of toluene diisocyanate, as compared to SAG factors of 2.8 to 3.2 for soft latex foam rubber. Recently, high resiliency (HR) foams have been developed. These foams are based on high primary hydroxyl containing polyether triols and polymeric isocyanates. Because of the markedly different polymer structure, foams of this type have quite different cushioning properties from the conventional urethane foams. The modulus of the new HR materials is much lower for a given density, and their compression deflection curve more closely resembles that of latex foam rubber. Such HR foams have SAG factors of 2.5 to 2.8. However, such new materials have a disadvantage in that the HR foams are considerably more costly on the board foot basis then conventional polyurethane foams.
Another important aspect of the sleep inducing pillow is that it must have a high degree of air permeability. In other words, it must allow the body heat to be readily dissipated as the person's head changes position and induces a pumping action in the pillow. Since all foams are insulating materials, the body heat cannot be readily removed by conductance.
Polyurethane foam presents a particular problem in this regard, because of the relatively lower air permeability of polyurethane foam compared to that of the latex foam rubber. Many urethane formulations even produce a partially "hermetic" foam (partially containing closed cells) which has to be "crushed" by intensive rolling or pounding to remedy its tendency to feel sluggish. This is notably the case when attempts are made to produce a very soft foam, e.g., of a ILD below 8 or 10 lbs., needed to make a bed pillow.
One of the approaches has been to produce a somewhat firmer foam and to "convolute cut" it. This is done by distorting the material, in sheet foam, between rolls which are studded over their entire surface with pyramidal projections in such a manner that the projection of one roll corresponds to the absence of a projection on the other roll. A band knife arranged in parallel to the axis of the rolls and close to the nip on the exit side of the compression-distorted material cuts the material into two matching layers which have over their entire surface a convoluted configuration. As an example, a two inch thick pad may be cut into two convoluted layers, where the peaks are 11/2" high and the valleys 1/2". Convolute cut material indeed possesses a lower ILD than the material from which it was cut. However, because of the concentration of stress on the tips of the pyramids when compressive and especially dynamic load is applied, the convoluted material tends to soften and collapse, i.e., lose height.
In the present invention, it has been found that an adequate reduction in initial ILD (an adequate increase in initial softness) for the creation of a satisfactory bed pillow can be accomplished by perforating the polyurethane material, rather than by convoluting it. Preferably, the holes (perforations) have a cross-sectional diameter between 1/8" and 1/2" and an equidistant spacing from 3/4" to 11/2". By this arrangement, the percentage of surface area that has been removed is not more than 30%. In the invention, it has been found that perforation in the above manner not only (a) increases the air permeability of the pillow, and (b) breaks up the surface tension of the foam blank in such a manner that deformation of the pillow under localized load does not extend to the entire surface, (a very important feature in reducing "fight back") but also permits to lower the ILD of the material without seriously affecting the ability of the material to withstand dynamic loading. Thus, in comparing a convoluted and a perforated foam by subjecting them to the Dynamic Fatigue Test, ASTM Designation D 1564-71, Suffix H, Procedure 8 (Dynamic Fatigue by the Roller Shear at Constant Load), it is found that after 20,000 cycles a convoluted Polyether urethane foam with an original ILD of 6 to 9 lbs. has lost 13% of its height, while a perforated material has lost less than 6%.